Intraluminal, intracavity, intravascular, and intracardiac treatment and diagnosis of medical conditions utilizing minimally invasive procedures is an effective tool in many areas of medical practice. These procedures are typically performed using imaging and treatment catheters which are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated, such as the femoral artery. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which is used to locate and diagnose a diseased portion of the body, such as a stenosed region of an artery. The catheter may also be provided with a therapeutic device, such as those used for performing interventional techniques including balloon angioplasty, laser ablation, atherectomy and the like. Catheters are also commonly used for the placement of grafts, stents, stent-grafts, etc. for opening up and/or preventing closure of diseased or damaged vessels.
Catheters having ultrasound imaging and/or therapeutic capabilities are generally known. For example, U.S. Pat. No. 5,313,949, issued to Yock, the disclosure of which is incorporated herein by reference, describes an intravascular ultrasound imaging catheter having an atherectomy cutting device. Generally speaking, there are two predominant techniques used to position the therapeutic catheter at the region of interest within the body. The first technique simply involves directly inserting the catheter into a vessel and advancing the catheter through the branches of the vascular system by pushing and steering the catheter to enter a desired branch as the catheter is moved forward. The use of this technique typically requires that the catheter be equipped with an extremely flexible guidewire at its distal tip which can be aimed in different directions by rotating the catheter or by actuating a steering mechanism.
The second technique utilizes a separate guidewire which is first positioned within the vascular system such that a distal end of the guidewire extends beyond the region of interest. The guidewire is routed into position by inserting it into a vessel and advancing it through the vascular system by pushing and steering the guidewire similar to the method previously described for a catheter. The catheter being inserted includes a guidewire lumen which is sized to receive the guidewire. The guidewire lumen may extend the entire length of the catheter, or alternatively, the guidewire lumen may be a short length lumen disposed at the distal end of the catheter. Once the guidewire is in place, the therapeutic and/or imaging catheter is routed over the guidewire to the region of interest while holding the guidewire fixed in place.
The use of a guidewire provides several advantages. Routing a catheter or guidewire through a circuitous path of the complex network of blood vessels to a region of interest can be a tedious and time consuming task. Placement of the guidewire is made even more difficult with increasing vessel occlusion which may occur in the later stages of vascular disease. In addition, many catheter procedures require the use of several different catheters. For instance, an imaging catheter may be initially inserted to precisely locate and diagnose a diseased region. Then, the imaging catheter may be removed and a therapeutic catheter, such as an balloon angioplasty catheter, may be inserted. Additional therapeutic or imaging catheters may be employed as necessary. Accordingly the successive insertion and removal of each of these catheters, called catheter "exchanges," is required because there is only enough space within the vessels to rout a single catheter at a time. Hence, with the use of a guidewire, the tedious and time consuming task of routing a device to the region of interest need only be done once. Then, the much easier procedure of routing catheters over the guidewire to the region of interest may be performed as many times as the desired therapy dictates.
In order to locate the site of interest and facilitate proper placement of the guidewire, and further to observe the site during and after treatment, a guidewire may include an imaging device, commonly a rotating ultrasonic imaging transducer or a phased-array ultrasound transducer. Providing the guidewire with imaging capability may eliminate the need for insertion of an imaging catheter or imaging capabilities in the therapeutic catheters. Hence, an imaging guidewire can reduce the number of catheter exchanges that a physician must do during a surgical procedure.
Imaging guidewires have been disclosed generally, for example, in U.S. Pat. No. 5,095,911, issued to Pomeranz, the disclosure of which is incorporated herein by reference. The imaging guidewire disclosed in Pomeranz includes an elongate, flexible body. A housing enclosing a rotating transducer is secured to the distal end of the body. A drive shaft extends through a lumen of the body and is coupled to the transducer. In order to image a different region of interest, the entire guidewire is moved back and forth to position the housing and transducer adjacent the region.
However, once the physician has carefully placed the imaging guidewire, it is preferable to maintain the guidewire in a fixed position so as not to lose the correct placement of the guidewire. At the same time, it is often desirable to obtain images along an axial length of diseased area. This currently requires axial translation of the imaging device by axially translating the entire guidewire. The problem with advancing and pulling back the imaging guidewire is that the correct placement of the guidewire may be lost and the physician must then spend more time repositioning the guidewire.
Furthermore, there are significant technical obstacles in producing an imaging guidewire having a sufficiently small diameter to fit within a guidewire lumen of a catheter while at the same time exhibiting the necessary mechanical and electrical characteristics required for placement in the vascular system and generation of high quality images. For instance, on typical catheters sized to be inserted in the smaller coronary vessels, the guidewire lumen is sized to receive a guidewire having a maximum diameter of 0.035". In addition, the 0.035" guidewire must have sufficient flexibility to traverse a tortous path through the vascular system, and also have sufficient column strength, or pushability, to transmit a pushing force from a remote proximal end of the guidewire, along a winding path, to the distal end thereof.
Moreover, if a rotating transducer is utilized, the drive shaft extending to the transducer must have stable torsional transmittance in order to achieve high quality images. Hence, the drive shaft must not only be flexible, but also must be torsionally stiff to limit angular deflection and nonuniform angular velocity which can cause image distortion. The drive shaft must also be mechanically and electrically connectable to a motor drive and transducer signal processing electronics. The connection must be easily disconnectable so that a guidewire lumen of a catheter may be threaded over the proximal end of the guidewire. This requirement also limits the size of the connector on the drive shaft because the connector must also fit through the guidewire lumen. The drive shaft and connector must also provide a high quality transmission of imaging signals between the imaging device and the signal processing equipment.
Therefore, a need exists for an improved imaging guidewire which overcomes the aforementioned obstacles and deficiencies of currently available guidewires.